The present application claims priority under 35 U.S.C. xc2xa7119 to Korean Application No. 2001-23515 filed on Apr. 30, 2001, which is hereby incorporated by reference in its entirety for all purposes.
1. Field of the Invention
The present invention relates to a linearity tester for an analog to digital converter and a method of testing an analog to digital converter for linearity, and more particularly to an apparatus and a method for testing linearity of an analog to digital converter without being influenced by noise.
2. Description of the Related Art
Generally, analog to digital converters have been developed and commonly used in digital devices, such as microprocessors and application specific integrated circuits (ASIC). The following items may be considered when testing an analog to digital converter: (1) an offset error in the analog to digital converter, which is a constant error irrelevant to input voltage; (2) a gain error that is included at a constant ratio to the input voltage; (3) an integral non-linearity error, which is seen in the output of the inverter as a variation of a curve deviated from an idealized straight line for a given input; (4) a differential non-linearity error, which is seen as a difference in the output of the converter that is due to an input voltage of an adjacent or previous input code; and (5) a MISS code, which is seen as the lack of an output of the converter in response to an analog input voltage applied to the analog to digital converter. Currently, in order to test an analog to digital converter with a logic tester, the only alternative is to purchase and use a tester that is optionally provided by the manufacturer of the analog to digital converter.
In FIG. 1, a conventional linearity tester for an analog to digital converter is illustrated. As shown in FIG. 1, the linearity tester for an analog to digital converter includes a controller 20 that outputs a resolution control signal to convert an analog signal to a digital signal, that provides control to test linearity of the digitized signal and that provides control to display a test signal; a signal generator 10 for generating a triangular wave signal; an analog to digital converter 12 for converting an analog triangular wave signal generated by the signal generator 10 into a digital signal and providing the digital signal as an output; a memory 14 for storing a code value digitized by the analog to digital converter under control of the controller 20; a histogram producer 16 for receiving the digitized code value from the memory 14 and generating a histogram under control of the controller 20; and a display 18 for displaying the histogram generated by the histogram producer 16 under control of the controller 20.
The signal generator 10 generates a triangular wave signal that is provided to the analog to digital converter 12. At this time, if the controller 20 inputs a sampling frequency clock to the analog to digital converter 12, the analog to digital converter 12 converts the analog triangular wave signal generated by the signal generator 10 into a digital signal according to the sampling frequency clock, and outputs the digital signal from the lowest level digital code to the uppermost level digital code step by step. Then, the controller 20 controls the memory 14 to store the digitized code converted by the analog to digital converter 12. Next, the controller 20 controls memory 14 so that the digitized code value stored therein is read out and provided to the histogram producer 16, which produces a histogram related to the digitized code value. The controller 20 controls the display 18 to display the histogram related to the digital code value. As an alternative, the digitized code value read from the memory 14 can also be made into a histogram using software, whereby the software generated histogram is thereafter displayed at the display 18.
The histogram illustrated at the display 18 is checked to evaluate linearity, with reference to the digitized code. The items considered for evaluation are differential nonlinearity, integral nonlinearity and the occurrence of a missing code. However, one of the problems associated with a conventional linearity tester for an analog to digital converter as described above is that the conventional tester cannot accurately test the linearity of the analog to digital converter, because the conventional tester is greatly influenced by noise having a higher level of resolution.
The present invention is therefore directed to an apparatus and method for testing linearity of an analog to digital converter, which substantially overcome one or more of the problems due to the limitations and disadvantages of the related art.
It is therefore an object of the present invention to provide a linearity tester for an analog to digital converter, and a corresponding method thereof, that accurately test linearity of an analog to digital converter without being influenced by noise.
It is another object of the present invention to provide a linearity tester for an analog to digital converter, and a corresponding method thereof, that minimize the influence of noise using a digital filter.
In order to accomplish the above noted and other objects, a linearity tester for an analog to digital converter of an embodiment of the present invention includes a controller that outputs a resolution control signal to convert an analog signal into a digital signal, that provides control to test linearity of the digitized signal and that provides control to display a test signal; a signal generator that generates a triangular wave signal; an analog to digital converter that converts the analog triangular wave signal generated by the signal generator into a digital signal and that outputs the digital signal; a memory that stores the digitized code value converted by the analog to digital converter under control of the controller; a digital filter that digitally filters and outputs the digital code value read out of the memory under control of the controller; a histogram producer that receives the digitized code value filtered by the digital filter and that generates a histogram responsive thereto; and a display that displays the histogram generated by the histogram producer under control of the controller.
In order to accomplish the above noted and other objects, a linearity tester for an analog to digital converter of a further embodiment of the invention includes a controller that outputs a sampling frequency clock to convert an analog signal into a digital signal, that digitally filters the digitized code value, that generates a histogram responsive to the digitally filtered signal according to a predetermined program, and that provides control to display the histogram; a signal generator that generates a ground voltage and an analog triangular wave signal; an analog to digital converter that converts the analog triangular wave signal generated by the signal generator into a digital signal and that outputs the digital signal; a memory that stores the digitized code value provided by the analog to digital converter under control of the controller; and a display that displays the histogram related to the digitally filtered code value generated under control of the controller.
In order to accomplish the above and other objects, a method for testing the linearity of an analog to digital converter of a further embodiment of the present invention includes generating a ground voltage; converting the ground voltage into a digital voltage value using the analog to digital converter; determining a filter order responsive to the digital voltage value; generating a digital filter value based on the determined filter order; converting an analog triangular wave signal into a digital code value using the analog to digital converter; digitally filtering the digital code value using the generated digital filter value to eliminate noise from the digital code value; and generating a histogram responsive to the filtered digital code value, to analyze linearity of the analog to digital converter.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.